Field of the Invention:
The invention relates to a sensor arrangement with a sensor body and two connection wires, for measuring the temperature of a medium in a motor vehicle, wherein the sensor body is electrically insulated from the medium by means of a covering which completely surrounds the sensor body.
Temperature sensors, in particular for measuring the temperature of media, such as oil or cooling liquid in a motor vehicle, generally change their electrical properties depending on the prevailing temperature. For example, when a sensor component which is composed of carbon or a semiconductor material is heated, the electrical resistance of said sensor component falls. Therefore, the temperature can be determined fairly accurately by measuring the resistance in the region of the large increase. Materials of this kind conduct the current better when they are hot than when they are cold, and are therefore also called NTC (Negative Temperature Coefficient) thermistors. Metals, such as platinum for example, exhibit the opposite effect and are therefore called PTC (Positive Temperature Coefficient) thermistors.
The sensor resistor, which is directly surrounded by medium, is generally connected to a supply voltage by way of its two connections which can be designed as pins or legs. The voltage which is dropped across one sensor resistor is determined and evaluated in a controller.
Heat can be introduced from the medium to the sensor by means of the two connection legs and at the same time by means of the side faces of the sensor module. In this case, that area of the arrangement which transmits heat is large, and therefore the response time of the measurement process is short. However, the risk of a short circuit between the connection legs is high, in particular owing to chips as can quite possibly be produced in a motor or a transmission by friction between the rotating parts.